You don’t need continual replanting - they have seeds, remember? A later seral stage forest has typically gone through the thinning phase, where the best trees out-compete the others and choke them out. Anything that germinates now needs to compete with the overstory.
As an aside, we can only really effectively use trees for sequestration in areas that were not productive forest before. That is, you can’t clear cut a bunch of shit, disturb the soil, and make an oil sands project and hope to come out ahead in terms of emissions/sequestration lost (without even considering oil production emission). Reclamation can help you get back to where you were, maybe… But to out perform a natural system is a tall order.